Transmission

ABSTRACT

An automatic transmission providing variable speed ratio and reverse drives between drive and driven shafts and including friction-engaging devices, in the form of friction clutches and brakes, for establishing the drives. The devices are operable by hydraulic servomotors, certain servomotors each having first and second pistons arranged in tandem, with the first piston being movable by hydraulic fluid to engage the associated friction device, the second piston being movable by hydraulic fluid to also move the first piston during the application of hydraulic fluid to the first piston to thereby substantially double the effective area of the pistons of the servomotor to provide additional increased pressure to the engaged friction device. The transmission also includes an hydraulic governor fixed to the driven shaft by a locking spring clamp connector positively holding and keying the governor to the shaft in a simple assembly operation and in a manner to insure sealing between fluid-passage ports in the shaft and in the governor body for transfer of activating hydraulic fluid.

ite States Patent [191 Clauss, Jr. et al.

[ Apr. 16, 1974 TRANSMISSION [73] Assignee: Borg-Warner- Corporation,Chicago,

Ill. 1

221 Filed: DeC.4,1972' 21 Appl.No.:312,179

Related U.S. Application Data A [62] Division of Ser. No. 67,326, Aug.27, 1970, Pat. No.

Primary ExaminerLeonard H. Gerin Attorney, Agent, or Fir mWilliam S.McCurry 57] ABSTRACT An automatic transmission providing variable speedratio and reverse drives between drive and driven shafts and includingfriction-engaging devices, in the form of friction clutches and brakes,for establishing the drives. The devices are operable by hydraulicservomotors, certain servomotors each having first and second pistonsarranged in tandem, with the first piston being movable by hydraulicfluid to engage the associated friction device, the second piston beingmovi able by hydraulic fluid to also move the first piston (g1. duringthe application of hydraulic fluid to the first [58] F ld f S 74/763 7piston to thereby substantially double the effective y le earc area ofthe pistons o the servomotor to provide addb tional increased pressureto'the engaged friction de- [561' References Clted vice. Thetransmission also includes an hydraulic gov UNITED STATES PATENTS ernorfixed to the driven shaft by a locking spring 3,053,117 9/1962 Hensel74/763 clamp connector positively holding and keying the 3,5 6/1governor to the shaft in a simple assembly operation 3,678,783 7/1972and in a manner to insure sealing between fluid- 3,706,24O 12/1972Borneman et al. 74/869 p g ports in the Shaft and in the governor y fortransfer of activating hydraulic fluid.

14 Claims, 4 Drawing Figures 71 a a! 1O 75 765? 23 68 1 M, Meg/82 58 2425 58 nmmmwmvw x191 \IWQI \x AM/I 1, 63,27 64 102 108 72 l I, I l 74 11% i so 1 a4 10 17 90 968 44 31 n 5 92 A L a 124 If s 12 1 99 455% man.39% 4o %I I %L TRANSMISSION SUMMARY OF THE INVENTION This inventionrelates to transmissions, and more particularly to such transmissionsemploying hydraulicallyoperated friction-engaging devices forestablishing forward speed ratio and reverse drives of the transmission,and speed-responsive means controlling hydraulic operation of at leastone of the devices.

In automatic transmissions, friction-engaging devices, in the form ofbrakes and clutches assemblies, have their drive and driven frictionelements engaged by pistons of hydraulic servomotors to establishforward and reverse drives of the transmission. It is important that thedrive and driven friction elements be engaged with the proper hydraulicforce by the servomotors to insure retention of the selected drive. Inparticular, in reverse drive with certain planetary gear sets as withthe one disclosed herein, in reverse drive the friction elements musthandle a torque load much higher than in forward drive. For thispurpose, a servomotor apply piston having a large effective area,exposed to hydraulic pressure, is desirable for reverse drive; but thissize piston is frequently unacceptable due to space limitations for thetransmission in the automobile.

Another object of the invention is to provide an improved hydraulicservomotor for. a' drive-control friction-engaging device in the form ofa clutch and in which large and small pistons are disposed in ahydraulic cylinder with the large piston'engaging the friction devicefor reverse drive and the-small piston engaging the large piston inforward drive,,and actuatable by hydraulic fluid to move the largepiston to engage the device with light pressure. In this way, sufficientengaging drives, and a hydraulic servomotor controlling operation of thedevice and including spaced chambers having pistons arranged to providecumulative working areas exposed to fluid under pressure flowing intothe respective chambers from separate passages connected 7 to a pump sothat the servomotor is effective to operapressure is provided forreverse, however, a smaller effective piston area is used in forward toprevent the harsh shifting which would result if the same engaging forcewas used for forward drive. The additional force is unnecessary due tothe smaller-torque being transmitted in forward drive. i

An object of the invention is to provide improved hydraulic servomotorsfor friction-engaging devices, such as clutches and brakes. A v

Another object of the invention is to provide improved hydraulicservomotor for drive-control frictionengaging device in the form of abrake in which dual pistons are disposed in a hydraulic cylinder withthe one piston engaging the friction deviceand the other piston engagingthe one piston and actuatable by hydraulic fluid to move the one pistonto engage the device with light pressure for forward drive; and inreverse drive both pistons having hydraulic fluid applied thereto toengage the device with an application of a I tive rapidly in applyingand releasing the device.

Another object of the invention is to provide an improved mechanism forassemblying an hydraulic governor and a shaft to positively hold thegovernor on the shaft in a manner insuring aligning the hydraulic portsof the governor shaft while inhibiting any tendency of the governor tovibrate.

Another object of the invention is to provide an improved and simplifiedassembly of an hydraulic governor and shaft, including a split springring clip disposed within a circular groove in an annular wall of thegovernor and having one end bent to extend radially inwardly through thegovernor wall into a recess in the shaft to key the governor to theshaft.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of atransmission incorporating the improvements of the present invention;

FIG. 2 is an enlarged cross-sectional view in detail of part of thetransmission;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1; and

FIG. 4 is a schematic view of a control system for use with thetransmission of FIG. 1.

Referring to FIG. 1, a transmission mechanism 10 is illustrated andincludes a transmission casing or case 11, an input shaft 12 and anoutput shaft 13. Fixed in the case 11 is a stationary sleeve 15 whichhas incorp'o rated therein several of the friction engaging mecha-'nisms for the transmission mechanism. Alsoprovided in the transmissioncase 11 are a plurality of frictionengaging devices including a pair offriction clutches 20 and 21, friction brake mechanism 23, 24, and 25,and a planetary gear set 27. An intermediate shaft 30 interconnectsclutch 20 with an annulus or ring gear 31 in the gear set, anintermediate shaft 34 interconnects clutch 21 with a double sun geararrangement 36 for the gear set 27. The planetary gear set 27 furtherincludes a planetary gear carrier 38 having planetary pinions 39journalled thereon and a planetary carrier 40 having planetary pinions42 journalled thereon. The planetary pinions 42 mesh with the annulusgear 31 and the sun gear 36. There is further provided an annulus orring gear 44 meshing with planetary pinions 39. A cylindrical torquetransmitting member or sleeve 63 is provided which interconnectsplanetary carrier 40, annulus gear 44, and output shaft 13. Slots 64 areprovided in one end of the member 102 for engagement by teeth 65 onoutput shaft 13. The planetary carrier plate 66 is provided with teeth67 received within axially extending grooves 68 in the sleeve 63, whichgrooves also receive splines 69 on ring gear 44. A split retainer ring70 is received within opposed circumferentially extending grooves in thesleeve 63 and ring gear 44 to hold the ring gear 44 and sleeve .63 inassembly. I

A hydraulic servomotor 50 is'provided for clutch 20 and a hydraulicservomotor 52 is provided for clutch 21. A hydraulic servomotor 54 isprovided to friction brake 23, and a hydraulic servomotor 55 is providedfor friction brake 24. A hydraulic servomotor58 is provided at the rearof the transmission case 11 for the friction brake mechanism 25. Aone-way brake 60 is provided for the planetary carrier 38, and a one-waybrake 62 is provided between friction brake 24 and intermediate shaft34.

Operation of the transmission mechanism as described above and relatingto the schematic showing in FIG. 1 is as follows: when clutches and 21are disengaged, a neutral condition is established.

Low or first speed ratio drive ratio is established by application ofclutch 20 connecting shaft 30 with input shaft 12 thereby drivingannulus gear 31 in the forward direction. The planetary carrier 40 isconnected to output shaft 13 thereby providing a forward drive of theoutput shaft 13 at a reduced speed, one-way brake 60 holding planetarycarrier 38 to provide a reaction element for the planetary gear set. Amanual first speed drive ratio, similar to the one-way drive justdescribed, may be provided by engagement of friction brake by means ofhydraulic servomotor 58 holding planetary carrier 38 against rotation ineither direction thereby establishing a two-way drive through theplanetary gear set.

Second speed ratio drive is provided by clutch 20 remaining engaged andby engagement of friction brake 24 by hydraulic servomotor 55 thusholding the sun gears 36 stationary. Under these conditions, a higherspeed forward drive is provided by the planetary carrier 40 drivinginput shaft 12 at a reduced speed with oneway brake 62 being madeeffective to hold the sun gears 36 stationary establishing a one-waydrive connection for second speed ratio. Optionally, brake 23 may beapplied to hold shaft 34 against rotation in either direction to providea two-way second speed ratio drive. I

Third speed ratio drive is provided by clutch 20 remaining engaged andclutch 21 being engaged by hydraulic servomotor 52 thereby lockingshafts 34 and together and locking up the planetary gear set andproviding a 1:] forward drive of the output shaft 13.

Reverse drive ratio is established by engagement of clutch 21 andengagement of friction brake 25, the sun gear 36 thus being driven in aforward direction, planetary carrier 38 being held stationary and thusdriving annulus gear 44 and thereby output shaft 13 in the reversedirection.

Referring to FIG. 1, the improved hydraulic servomotor 52 foraccomplishing the operation of the friction clutch 21 is designed toprovide sufficient pressure by its piston assembly to insure engagementof the clutch during varying torque-transmission ratios provided by theplanetary gearing and its brake and clutch controls. More particularly,during establishment of reverse drive, the torque transmitted throughclutch 21 is considerably higher than the torque transmitted in thethird speed or direct drive ratio when clutches 20 and 21 share thetorque load. Accordingly, it is imperative that the friction clutch 21be engaged with greater pressure during reverse drive than the pressureapplied during third speed ratio.

Describing the clutch and servomotor mechanism, an annular drum 71 hasits radially inner face of its outer wall provided with splines 72formed therein for receiving tangs 73 on friction plates 74 and abacking plate 75. Friction plates 74 are interleaved with frictionplates 76 and are splined to the cylindrical portion 78 of a member 77,the member 77 having a disc-like end portion 78 splined to the drum 79of clutch 20 to form a backing plate, which has its radially inner edgekeyed to the drive shaft 12. The drum 71 has a radially inner peripheralcylindrical portion 18 in splined engagement with the end of the sleeveshaft 34, so that upon the clutch plates 74, and 76 being engaged by theservomotor 52, rotation of drive shaft 12 will rotate the sleeve shaft34.

The servomotor 52 comprises annular pistons 80 and 81 of different sizesand respectively mounted in a common cylinder including large and smallchambers 82 and 83 in drum 71, chamber 83 being defined by spacedcylindrical walls 84 and 85 and a radially extending wall 86 connectingthe walls 84 and 85, and chamber 82 being provided by spaced inner andouter cylindrical walls 85 and 87 and radial wall 88, as well as piston81 which engages the piston 80. A coil spring 9 has one end seatedagainst the piston 80 and its other end engaging a spring seat 90secured on the drum portion 18 so that the spring is operative to urgethe pistons 80 and 81 to the positions shown in FIG. 1.

Packing rings 91 prevent leakage of fluid from the chamber 83 around theouter and inner faces of piston 81 into the chamber 82 and from chamber83 into chamber 82, while packing rings 92 prevent leakage of fluid fromthe chamber 82 around the outer and inner faces of piston 80 into thedrum.

Pistons 80 and 81 are provided with centrifugallyoperated relief valves96 and 97 for controlling the release of fluid from the chambers 82 and83 and including balls 98 and 99 operable to close drain passages in thepistons when the balls are urged by fluid under pressure in thechambers, and to open the passages when pressure is relieved andcentrifugal force causes the balls to move to open the passages.

To provide fluid under pressure to the chambers 82 and 83 to actuatepistons 80 and 81, spaced passages 93 and 94 are formed in thecylindrical wall 85 of the drum respectively communicating with chambers82 and 83 and also with spaced annulus grooves in the stationary sleeve15 connected to suitable valving schematically illustrated in FIG. 4operable to selectively control flow of fluid under pressure from anengine driven pump 131 to either the passage 93 or to both passages 93and 94.

In the operation of clutch 21 to provide third speed ratio or directdrive, when the clutch 20 is also engaged, liquid under pressure isdirected to the passage 94 and to chamber 83 to move piston 81 andthereby abutting piston 80 to engage the clutch plates 74 and 76. Itwill be noted, that at this time, chamber 82 is devoid of fluid so thatthe piston 81 must contact the piston 80 to move the piston 80 and thefriction clutch plates. Reverse drive is obtained by engaging clutch 21and brake 25. To obtain reverse drive and to insure maintenance of theincreased engaging force required of this drive, clutch 21 is engaged byfluid under pressuredirected to the passages 93 and 94 and into chambers82 and 83 to apply fluid under pressure to piston 80 and therebymaterially increase the force applied to the clutch plates to engage theclutch 21. This will be apparent because the larger effective area ofpiston 80 is subject to fluid under pressure. The fluid under pressureapplied to the smaller effective area of the piston 81 is balanced bythe pressure of fluid in chamber 82.

Referring to FIGS. 1 and 2, and as previously described, the improvedhydraulic servomotor 58 is effective to-operate the brake 25 to providea two-way drive in the first or low speed ratio, when the clutch isengaged. Also, the servomotor 58 is operative to engage the brake 25 forreverse drive, when the clutch 21 is engaged. The servomotor 58comprises a piston 100 axially slidably mounted in an annular largechamber 101 in a hydraulic cylinder 102 and engaging an annularthrust-transmitting member 103 providing a connection between piston 100and pressure apply plate 104 of brake 25. The piston 100 urged to theright by a coil spring 105 having one end seated against a retainingring 106 fixed to the cylinder 102. A member in the form of a drum 107is slidably positioned within a smaller chamber 101 of cylinder 102 withits rim 108 engaging the radially outer surface of the chamber and itsinner periphery having a seal 109 engaging the axially extending wall110 of piston 100.

On the side of drum 107 remote from piston 100 is a second piston 111abutting piston 100. The piston 100, drum 107 and piston 1 11 areannular in configuration, and an axially extending wall 110 of piston100 has its peripheral edge abutting the piston 111. A'seal 112 isdisposedbetween the piston 100 and case 102. Suitable seals 113 and 114are disposed within grooves in the inner and outer peripheral edges ofpiston 111 and engage the inner surface of the cylinder 102 and the rim108 of drum 107. Hydraulic fluid supply passages 115 and 116 areprovided in the casing 11, the passage 115 terminating in a port 117 inchamber 101 between the piston 100 and drum 107 and the passage 116terminating in a port 118 providing fluid between the right end of thecylinder chamber 101a andpiston 1 11. Accordingly, fluid under pressureflowing through the two ports 117 and 118 into the chamber 101a areseparated by the drum 107 so that the fluid entering port 117 acts onlybetween piston 100 and drum 107 and fluid entering port 118 is operativeto act only on piston 111.

Servomotor 58 may be actuated by valving 130 to selectively supplypressure to passage 115 or toboth passages 115 and 116 as will now bedescribed. In operation of servomotor 58 to engage brake 25 to providetwoway drive in first or low speed ratio with clutch engaged, fluidunder pressure is directed by suitable valving 130 to passage 115 andthrough port 117 to cause piston 100 to move to the left to engage thebrake. To obtain reverse drive, when clutch 21 is engaged, considerablygreater force is exerted by the servomotorto engage the brake sincefluid under pressure is directed to passage 116 and port 118, as well asto passage 115 and port 117, to move pistons 100 and 111 in tandem toapply the brake 25, due to the double area of pistons 110 and 111, actedupon by the fluid under pressure.

As advantageous feature of the servomotor '58 is the sive to the speedof rotation of the driven shaft to provide a signal pressure variablewith thespeed of the driven shaft to the valving 130 for controlling thebrakes and clutches to provide automatic shifting between first, second,and third speeds. An improved assembly of the governor 120 and shaft 13is provided to securely fasten the governor to the shaft. Moreparticularly, the shaft 13 and the governor 120 are in telescopingrelation as the shaft extends through the governor. The governor has itshousing or body 121 formed at one end with a circular flange 122provided with an an nular groove 123 receiving a resilient split member124 in the form of a spring retainer wire having one end bent to providea tab 125 extending inwardly into a radially drilled hole 126 in theshaft 13. It will be noted that the end of the keying tab 125 engagesthe bottom of hole 126 in the shaft and allows the member 124 to be freeof the body adjacent to the tab so that a side loading effect isachieved. This feature is advantageous as the governor body is heldtight to one side of the shaft in order to obtain better sealing betweenthe fluid flow passages in the shaft and the ports in the governor body.It may be noted that this assembly provides positive keying and accurateaxial location of the governor on the shaft by a relatively simplemanual operation. Also, by virtue of the spring clamping action plus theability of the retainer to wrap itself about the shaft, any tendency tovibrate is inhibited. Proper assembly and seating of the retainer isreadily determined by quick visual inspection requiring no gauging.

While there has been shown the improved assembly of an hydraulicgovernor and a shaft, it is to be understood such disclosure is only byway of example, as it is obvious that the concept may be used in avariety of many other uses, such as keying a spur gear to a shaft.

Various features of the invention have been particularly shown anddescribed; however, it should not be limited to the specificconstructions and arrangements disclosed except only insofar as theappended claims may be so limited, as it will be apparent to thoseskilled in the art that changes may be made without departing from theprinciples of the invention.

rapid application and release of the brake 25 for re- 1 What is claimedis:

1. A transmission comprising a driving element; a driven element;gearing between said elements; and control means for said gearingincluding first and second friction engaging devices adapted toestablish at least one forward speed ratio drive and reverse drive; andfirst and second hydraulic servomotors respectively associated with andoperative to apply said devices, each of said servomotors having anhydraulic cylinder with first and second chambers, first and secondpistons axially movable in said chambers with said first piston beingengageable with the associated device and said second piston contactingsaid first piston.

2. A transmission as defined in claim 1 wherein said firstfriction-engaging device is a friction clutch, and said secondfriction-engaging device is a friction brake.

3. A transmission as defined in claim 1 wherein said first chamber andpiston of each servomotor is relatively larger than said second chamberand piston.

4. A transmission as defined in claim 1 wherein said first chamber andpiston of each servomotor is relatively larger than said second chamberand piston, and said first friction-engaging device is a frictionclutch,

and said second friction-engaging device is a friction brake.

5. A transmission as defined in claim 1 wherein said gearing comprises aplanetary gear set.

6. A transmission is defined in claim 1 including centrifugal valveassemblies in said first and second pistons of said first servomotor andhaving balls closing drain holes in said pistons during application offluid under pressure in said pistons and operable by centrifugal forceto move to open said drain holes upon release of pressure fluid in saidpistons.

7. A transmission as defined in claim 1 including means for supplyingfluid under pressure to said second chamber of said first servomotor tomove said second piston therein and said first piston contacted therebyto engage said first device to establish said forward drive; and meansfor supplying fluid under pressure to both said chambers of saidservomotors to move said pistons to engage said devices to establishreverse drive.

8. A transmission as defined in claim 7 wherein said first chamber andpiston of each servomotor is relatively larger than said second chamberand piston.

9. A transmission comprising a driving element; a driven element;gearing between said elements; and control means for said gearingincluding first and second friction engaging devices adapted toestablish at least one forward speed ratio drive and reverse drive;

and first and second hydraulic servomotors respectively associated withand operative to apply said devices, each of said servomotors having anhydraulic cylinder with first and second connecting chambers, first andsecond pistons axially movable in said chambers with said first pistonbeing engageable with the associated device and said second pistoncontacting said first piston, and means for supplying fluid underpressure to said first chamber of said second servomotor to move saidfirst piston therein to engage said second device to establish saidforward drive.

10. A transmission as defined in claim 9 wherein said firstfriction-engaging device is a friction clutch, and said secondfriction-engaging device is a friction brake.

ing members between said elements; and control means for said gearingincluding first and second frictionengaging devices adapted to establishfirst and second forward speed ratio drives and reverse drives; andfirst and second hydraulic servomotors respectively associated with andoperative to apply said devices, each of said servomotors having anhydraulic cylinder with connecting first and second chambers, first andsecond pistons axially movable in said chambers with said first pistonsbeing engageable with the associated device and said second pistoncontacting said first piston; means for supplying fluid under pressureto said first chamber of said second servomotor to move said firstpiston therein to engage said second device to establish said firstforward speed ratio drive; means for supplying fluid under pressure tosaid second chamber of said first servomotor to move said second pistontherein said first piston contacted thereby to engage said first deviceto establish said second forward speed ratio drive; and means forsupplying fluid under pressure to said chambers of said servomotors tomove said pistons to engage said devices to establish reverse drive.

14. In a transmission, a drive shaft; a driven shaft; a shaftintermediate said drive and driven shafts; a sleeve shaft surroundingsaid intermediate shaft; a first friction clutch engageable to connectsaid drive and intermediate shafts; a second friction clutch engageableto connect said drive shaft to said sleeve shaft; a planetary gear setincluding a first ring gear connected to said intermediate shaft, .sungears connected to said sleeve shaft, a second ring gear connected tosaid driven shaft, planet gears connecting said ring and sun gears, acarrier for said planet gears and connected to said second ring gear; afriction brake engageable to prevent rotation of said planet gearcarrier; means for controlling said first and second clutches and saidbrake to provide a plurality of forward speed ratio drives and reversedrive including: a first hydraulic servomotor for engaging said firstfriction clutch; a second hydraulic servomotor for engaging said secondfriction clutch and including an hydraulic cylinder having connectingfirst and second chambers, first and second pistons on said chamberswith said first piston engaging said second clutch and contactable withsaid second piston; a third servomotor for engaging said friction brakeand including an hydraulic cylinder having connecting first and secondchambers, first and second pistons in said chambers, with said firstpiston engaging said brake and contactable with said second piston;means for supplying fluid under pressure to said first servomotor toengage said first friction clutch; means for supplying fluid underpressure to said first chamber of saidsecond servomotor to move saidfirst piston therein to engage said friction brake, when said firstmeans for supplying fluid under pressure to said second chamber of saidsecond servomotor to move said second piston therein and thereby saidfirst piston to engage said second clutch, when said friction clutch isengaged, to provide a second speed ratio drive; and means for supplyingfluid to both chambers of said second clutch to engage said secondclutch, and also to both chambers of said brake to provide said reversedrive.

1. A transmission comprising a driving element; a driven element; gearing between said elements; and control means for said gearing including first and second friction engaging devices adapted to establish at least one forward speed ratio drive and reverse drive; and first and second hydraulic servomotors respectively associated with and operative to apply said devices, each of said servomotors having an hydraulic cylinder with first and second chambers, first and second pistons axially movable in said chambers with said first piston being engageable with the associated device and said second piston contacting said first piston.
 2. A transmission as defined in claim 1 wherein said first friction-engaging device is a friction clutch, and said second friction-engaging device is a friction brake.
 3. A transmission as defined in claim 1 wherein said first chamber and piston of each servomotor is relatively larger than said second chamber and piston.
 4. A transmission as defined in claim 1 wherein said first chamber and piston of each servomotor is relatively larger than said second chamber and piston, and said first friction-engaging device is a friction clutch, and said second friction-engaging device is a friction brake.
 5. A transmission as defined in claim 1 wherein said gearing comprises a planetary gear set.
 6. A transmission is defined in claim 1 including centrifugal valve assemblies in said first and second pistons of said first servomotor and having balls closing drain holes in said pistons during application of fluid under pressure in said pistons and operable by centrifugal force to move to open said drain holes upon release of pressure fluid in said pistons.
 7. A transmission as defined in claim 1 including means for supplying fluid under pressure to said second chamber of said first servomotor to move said second piston therein and said first piston contacted thereby to engage said first device to establish said forward drive; and means for supplying fluid under pressure to both said chambers of said servomotors to move said pistons to engage said devices to establish reverse drive.
 8. A transmission as defined in claim 7 wherein said first chamber and piston of each servomotor is relatively larger than said second chamber and piston.
 9. A transmission comprising a driving element; a driven element; gearing between said elements; and control means for said gearing including first and second friction engaging devices adapted to establish at least one forward speed ratio drive and reverse drive; and first and second hydraulic servomotors respectively associated with and operative to apply said devices, each of said servomotors having an hydraulic cylinder with first and second connecting chambers, first and second pistons axially movable in said chambers with said first piston being engageable with the associated device and said second piston contacting said first piston, and means for supplying fluid under pressure to said first chamber of said second servomotor to move said first piston therein to engage said second device to establish said forward drive.
 10. A transmission as defined in claim 9 wherein said first friction-engaging device is a friction clutch, and said second friction-engaging device is a friction brake.
 11. A transmission as defined in claim 9 wherein said first chamber and piston of each servomotor is relatively larger than said second chamber and piston.
 12. A transmission as defined in claim 9 wherein said gearing comprises a planetary gear set.
 13. A transmission comprising a driving element; a driven element; gearing having a plurality of intermeshing members between said elements; and control means for said gearing including first and second friction-engaging devices adapted to establish first and second forward speed ratio drives and reverse drives; and first and second hydraulic servomotors respectively associated with and operative to apply said devices, each of said servomotors having an hydraulic cylinder with connecting first and second chambers, first and second pistons axially movable in said chambers with said first pistons being engageable with the associated device and said second piston contacting said first piston; means for supplying fluid under pressure to said first chamber of said second servomotor to move said first piston therein to engage said second device to establish said first forward speed ratio drive; means for supplying fluid under pressure to said second chamber of said first servomotor to move said second piston therein said first piston contacted thereby to engage said first device to establish said second forward speed ratio drive; and means for supplying fluid under pressure to said chambers of said servomotors to move said pistons to engage said devices to establish reverse drive.
 14. In a transmission, a drive shaft; a driven shaft; a shaft intermediate said drive and driven shafts; a sleeve shaft surrounding said intermediate shaft; a first friction clutch engageable to connect said drive and intermediate shafts; a second friction clutch engageable to connect said drive shaft to said sleeve shaft; a planetary gear set including a first ring gear connected to said intermediate shaft, sun gears connected to said sleeve shaft, a second ring gear connected to said driven shaft, planet gears connecting said ring and sun gears, a carrier for said planet gears and connected to said second ring gear; a friction brake engageable to prevent rotation of said planet gear carrier; means for controlling said first and second clutches and said brake to provide a plurality of forward speed ratio drives and reverse drive including: a first hydraulic servomotor for engaging said first friction clutch; a second hydraulic servomotor for engaging said second friction clutch and including an hydraulic cylinder having connecting first and second chambers, first and second pistons on said chambers with said first piston engaging said second clutch and contactable with said second piston; a third servomotor for engaging said friction brake and including an hydraulic cylinder having connecting first and second chambers, first and second pistons in said chambers, with said first piston engaging said brake and contactable with said second piston; means for supplying fluid under pressure to said first servomotor to engage said first friction clutch; means for supplying fluid under pressure to said first chamber of said second servomotor to move said first piston therein to engage said friction brake, when said first means for supplying fluid under pressure to said second chamber of said second servomotor to move said second piston therein and thereby said first piston to engage said second clutch, when said friction clutch is engaged, to provide a second speed ratio drive; and means for supplying fluid to both chambers of said second clutch to engage said second clutch, and also to both chambers of said brake to provide said reverse drive. 